OBSERVATIONS ON LARVAE OF CORETHRA PUNCTIPENNIS. 273 



this time of the year there is no loss from pupation and the losses 

 from other causes are not great enough to reduce the number of 

 these larvae very materially, so that the number remains uni- 

 formly high during this period of time. 



The ice usually disappears from the lake during the first week 

 in April and soon after this event the larvae begin to pupate. As 

 the temperature of the water rises, the rate of pupation increases 

 so that an appreciable decrease in the number of larva is noted 

 for the month of May. With the further advance of the season, 

 pupation becomes still more common and this results in a very 

 marked decrease in the number of Corcthra larvae in late June as 

 in 1916 and in 1918, or in early July as in 1917. This decline in 

 numbers continues until the minimum of the year is reached in 

 August, more especially during the first half of this month. A 

 minimum of 295 larvae per square meter was noted at Station II. 

 on August 2, 1917, while the average in March of this year was 

 a little more than one hundred times as large. (See Table I.) 



Small swarms *of adults appear in May and in early June, but 

 the great flights are correlated in time with waves of very active 

 pupation in late June, in July, and in early August. Thus, enor- 

 mous swarms appear from time to time during the latter period. 



During late August and especially in September there is a 

 slackening in the process of pupation and correlated with this is 

 an increase in the number of larvae. The increase is most marked 

 during the second half of September and in early October, but 

 the numbers do not reach the maximum point until November or 

 December. The largest number of larvae obtained in any of the 

 samples was 33-8oo individuals per square meter on December 

 21, 1917. 



Pupae were not noted in the samples of mud until about the 

 middle of June, or at the beginning of the more active period of 

 pupation ; thereafter they appeared regularly until late August. 

 A maximum of 2,890 pupae per square meter was found on June 

 28, 1917, while the second in rank was 1,370 individuals per 

 square meter on July 9, 1917. 



